1. Field of the Invention
The present invention relates to a formation method for forming finely-structured parts, using an isotropic etching process. Also, the present invention relates to a finely-structured part formed by the formation method, and a product using such a finely-structured part.
2. Description of the Related Art
With the recent advance of fine-structure-formation technology, it has attempted to provide higher function, higher performance, and additional value for various existing products, using the fine-structure-formation technology. Especially, at present, since it is possible to perform processing of finely-structured parts on a fine scale corresponding to the order of light wavelength, the trials are promising in various fields in which the finely-structured parts are necessitated.
For example, in the field of liquid crystal displays equipped with a back light unit, in order to increase brightness of the liquid crystal display, and in order to decrease electric power consumption of the back light unit, it is proposed that an array of micro-lenses be associated with a glass substrate of the liquid crystal display, with a size of each micro-lens being on the order of a pixel size of the liquid crystal display.
In particular, in the liquid crystal display, an aperture is formed in each pixel area to thereby introduce the light therethrough, but an area of the aperture is inevitably restricted due to an arrangement of wiring patterns and electrode patterns. Especially, in a TFT (thin film transistor) liquid crystal display of active matrix type, an aperture rate of the aperture area to each pixel area is less than 60%. Of course, the smaller the aperture rate, the darker the brightness of the liquid crystal display. Thus, before the brightness of the liquid crystal display can be made higher, it is necessary to increase the amount of light to be introduced into each pixel area, and thus the electric power consumption of the back light unit becomes larger.
However, if the micro-lens array is associated with the liquid crystal display so that the aperture rate is virtually increased at each pixel area, i.e. if the amount of light to be introduced into each pixel area is increased by the micro-lens array, it is possible to make the brightness of the liquid crystal display higher without the increase of the power consumption of the back light unit.
Also, it is proposed that an array of micro-lenses be assembled in a liquid crystal projector which may be used in a relatively light environment. In particular, in the liquid crystal projector, a liquid crystal display is used as a light-valve device having an array of light valves, and it is necessary to increase an amount of light passing through each light valve of the light-valve device before a projected image can be distinctly observed in the relatively light environment.
Japanese Laid-Open Patent Publication (KOKAI) No, 2001-201609 discloses a two-piece formation method as a process for forming an array of micro-lenses used in the liquid crystal projector. In particular, the micro-lens array is press-molded from a suitable uncured photo-curable resin on a suitable glass substrate, using a glass mold or matrix having an array of hemisphere-like micro-recesses formed in a molding face thereof. Then, the glass substrate carrying the molded micro-lenses is exposed to radiation of ultraviolet rays, thereby setting of the molded micro-lenses on the glass substrate. Thereafter, the glass matrix is removed, and the molded micro-lenses are left on the glass substrate, resulting in production of the micro-lenses arrayed on and adhered to the glass substrate.
Japanese Laid-Open Patent Publication (KOKAI) No. 2001-246599 also discloses another type two-piece formation method for forming an array of hemisphere-like micro-leases, In this two-piece type formation method, a matrix for molding the hemisphere-like micro-lens array is made from a silicon substrate exhibiting a superior flatness and an excellent processability.
Further, Japanese Laid-Open Patent Publication (KOKAI) No. 2001-074913 discloses a transferring formation method including a heating process and a dry etching process to form an array of hemisphere-like micro-lenses used in the liquid crystal projector. In particular, an array of circular masks, composed of a suitable thermal deformable material, is formed on a suitable glass substrate, and is subjected to the heating process such that each circular mask is thermally deformed into a hemisphere-like shape. Then, the glass substrate carrying the hemisphere-like masks is subjected to the dry etching process, so that an array of hemisphere-like micro-lenses is formed in the glass substrate as if the array of hemisphere-like masks are transferred to the glass substrate.
Furthermore, Japanese Laid-Open Patent Publication (KOKAI) No. 2001-147305 discloses an isotropic-etching formation method including a wet etching process to form an array of hemisphere-like micro-lenses used in a liquid crystal projector. In particular, a silicon mask layer is formed on a quartz glass substrate, and an array of circular openings is formed in the silicon mask layer. Then, the quartz glass substrate having the mask layer is subjected to the wet etching process, whereby a hemisphere-like recess is formed in the quartz glass substrate at each circular opening of the silicon mask layer. Thereafter, the silicon mask layer is removed, thereby obtaining a hemisphere-like micro-lens array.
Although the micro-lens array is used in the liquid crystal display of the liquid crystal projector whereby the projected image can be distinctly observed in a relatively light environment, it is proposed that the array of micro-lenses is assembled in a semi-permeation type liquid crystal display which is operated in either a permeation-display mode or a reflection-display mode, as disclosed in Japanese Laid-Open Patent Publication (KOKAI) No. 2000-298267.
The semi-permeation type liquid crystal display includes a reflection plate associated with a back light unit, and an array of apertures is formed so as to be registered with an array of pixels of the liquid crystal display, an area of each aperture being smaller than a size of each pixel. In the permeation-display mode, a displayed image is based, on the light emitting from the back light unit and passing through the apertures of the reflector plate. In the reflection-display mode, a displayed image is based on the light reflected from the reflection plate. Accordingly, in the semi-permeation type liquid crystal display, since an aperture rate of the aperture area to the pixel area is considerably restricted, it is advantageous to intervene the micro-lens array between the reflector plate and the back light unit to make the brightness higher in the permeation-display mode.
As another example of the finely-structured parts, there is a planar light wave circuit device as disclosed in “Optical Switching And Optical Interconnection”, written by Kenichi YUKIMATSU and published by KYORITSU PUBLISHING COMPANY. The planar light wave circuit device includes a quartz glass substrate having optical light guide paths, optical switches, optical couplers, optical splitters and so on formed therein. When the planar light wave circuit device is too miniaturized, light-transmission losses becomes larger, and wavelength-separation characteristics are deteriorated. Namely, the planar light wave circuit device has a limitation of miniaturization. Thus, the formation of the various optical elements must be performed by processing the quartz glass substrate having a relatively large area size.
Japanese Laid-Open Patent Publication (KOKAI) No. EHI-06-082832 discloses an active-matrix type liquid crystal display which includes a TFT (thin film transistor) substrate as a finely-structured part. In this TFT substrate, a wiring pattern is buried in the TFT substrate to smooth the surface of the TFT substrate, whereby liquid crystal molecules are more uniformly oriented, resulting in an improvement of display performance in the liquid crystal display.
Japanese Laid-Open Patent Publication (KOKAI) No. EHI-11-283751 discloses an organic electroluminescence device which includes a diffraction grating as a finely-structured part. The diffraction grating is assembled in the electroluminescence device to efficiently take out light from a luminescence layer of the electroluminescence device. The diffraction grating comprises a suitable substrate in which a plurality of fine grooves is regularly formed at a pitch corresponding to the order of a light wavelength. Namely, before the diffraction grating can be produced, it is necessary to process the substrate such that a sub-wavelength periodic structure is formed in the substrate.
Japanese Laid-Open Patent Publication (KOKAI) No. 2000-081625 discloses a liquid crystal display which includes a pair of alignment layers as a finely-structured part. In the liquid crystal display, a liquid crystal is confined in a space defined between the alignment layers such that the molecules of the liquid crystal are regularly oriented. Usually, the alignment layer is made of a suitable organic film, such as a polyimide film, and is produced by a rubbing method. In this method, the polyimide film is rubbed with, for example, a cotton cloth in a given direction, such that a plurality of fine grooves are regularly formed in a surface of the polyimide film. The rubbing method has drawbacks in that the polyimide film is susceptible to scratches and dust particles while being rubbed with the cotton cloth. Therefore, it is proposed that the alignment layer be made of an inorganic material. Namely, before the inorganic alignment layer can be produced, it is necessary to process an inorganic layer such that a submicron periodic structure is formed in the inorganic layer.
Japanese Laid-Open Patent Publication (KOKAI) No. 2001-074935 discloses an optical polarization element as a finely-structured part. Although the optical polarization element is usually made of an optical material exhibiting a polarization-anisotropy, it is possible to make the optical polarization element of an optical isotropic material. In particular, the latter optical polarization element includes a substrate made of the optical isotropic material, and an ultra-fine birefringence structure formed in the optical isotropic substrate. For the formation of the ultra-fine birefringence structure, it is possible to utilize a fine-structure-formation technology as disclosed in, for example, Applied Optics Vol.39, No 20, 2000).
As still yet another example of the finely structured parts, there is a chemical microchip used in a chemical analysis system, such as μTAS (Micro Total Analysis Systems), LOC (Laboratory On Chip) or the like, as disclosed in “Nano-Technology And Macromolecule” published by THE SOCIETY OF POLYMER SCIENCE, JAPAN. The chemical microchip includes a suitable substrate in which grooves and recesses are formed in the order of microns or tens of microns.
As discussed above, the fine-structure-formation technology can be applied to the various technical fields. In all cases, a substrate is processed to form a fine structure therein, thereby producing a finely-structured part. The processing of the substrate should be uniformly and equally performed before the fine structure can be formed in the substrate at high precision to thereby obtain the finely-structured part having a high-quality. Also, in order to inexpensively supply the finely-structured parts to a market, it is necessary to efficiently perform the production of the finely-structured parts at low cost.
The efficient production of the finely-structured parts is possible by using a large-sized substrate in which a plurality of fine structures are simultaneously formed. Namely, after the plurality of fine structures are formed in the large-sized substrate, it is divided into respective substrate sections having the fine structures, and thus it is possible to lower production cost of the individual finely-structured parts. However, conventionally, the large-sized substrate is not utilized for the reasons stated below.
For example, in the aforesaid two-piece formation method for forming the micro-lens array, it is difficult to produce a large-sized glass mold or matrix having a plurality of micro-recess arrays formed in a molding face thereof. Although the large-sized matrix is produced, when there is a thermal expansion difference between the large-sized matrix and the large-sized substrate, it is necessary to strictly control a processing-temperature during the production of the plurality of micro-lens arrays, such that thermal strains, based on the thermal expansion difference, can be eliminated from the plurality of micro-lens arrays as much as possible. Of course, it is very troublesome to strictly control the processing-temperature. Also, in the two-piece formation method, the plurality of micro-lens arrays is press-molded from a suitable uncured photo-setting resin on the large-sized substrate, using the large-sized matrix, and it is difficult to uniformly exert a pressure to the large-sized matrix.
In the aforesaid transferring formation method including the heating process and the dry etching process to form the micro-lens array, although it is possible to uniformly and equally process the large-sized substrate so as to form a plurality of micro-lens arrays in the large-sized substrate, facilities for performing the transferring formation method must have a large-scale for processing the large-sized substrate. Of course, large-scale facilities are very expensive, resulting in an increase of a production cost of the micro-lens arrays. Also, the facilities include a vacuum chamber for performing the dry etching process, and it takes too much time for evacuating the vacuum chamber, resulting in a lowering of production efficiency of the micro-lens arrays. Furthermore, it is practically impossible to process more than one large-sized substrate in the vacuum chamber.
In the aforesaid isotropic-etching formation method including the wet etching process to form the micro-lens array, it is possible to process the large-sized substrate to form a plurality of micro-lens arrays in the large-sized substrate at a relatively low cost, because an etching cell for the wet etching process is merely made larger such that the large-sized substrate is sufficiently received in an etching solution held therein. However, it is very difficult to properly control the wet etching process such that a whole of the large-sized substrate is uniformly subjected to the etching process. Namely, for example, it is difficult to maintain the entire etching solution at a given constant etching temperature when the large etching cell is used. Also, it is necessary to make the large-sized substrate of an expensive material containing substantially no impurities, such as quartz glass, silicon or the like, before the wet etching process can be properly controlled.
Similar matters are substantially true for the other finely-structured-parts, i.e. the planar light wave circuit device, the active-matrix type liquid crystal display, the organic electroluminescence device, the orientation film, the optical polarization element as a finely-structured part, and the chemical microchip.